An updated version of my muscle studies / Ref sheet from here (Old version will go into scraps):
http://www.furaffinity.net/view/14516802

Did a bit of refining and changes primarily to the back of the torso.

I'd recommend anyone who wants to draw muscle art to do something similar like this, look up anatomy references and bodybuilder pictures and try to compile a sheet with different views of body parts. You will find some refs "conflict" a bit here and there, that is in part because muscles are built slightly different from person to person.
But when you build your own sheet you have a good reference for how YOU draw them which both helps with some correctness of doing it but also consistency within your own work.

PS: This is a slightly different file than the one posted on FurAffinity, the nipples are only hinted at due to the age rating having to be higher if they were more pronounced.